Remove obsolete export
Remove obsolete export

The ‘Placement’ type has been moved to Types.hs but we kept exporting it
from Cluster, which is not needed.

grnet/snf-ganeti,apyrgio/snf-ganeti,andir/ganeti,onponomarev/ganeti,ganeti-github-testing/ganeti-test-1,onponomarev/ganeti,leshchevds/ganeti,andir/ganeti,ganeti/ganeti,bitemyapp/ganeti,leshchevds/ganeti,mbakke/ganeti,ganeti-github-testing/ganeti-test-1,apyrgio/ganeti,leshchevds/ganeti,andir/ganeti,ganeti/ganeti,apyrgio/snf-ganeti,apyrgio/ganeti,yiannist/ganeti,grnet/snf-ganeti,mbakke/ganeti,bitemyapp/ganeti,yiannist/ganeti,mbakke/ganeti,dimara/ganeti,yiannist/ganeti,dimara/ganeti,ganeti/ganeti